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The variable flexibility of a fish body is believed to play a significant role in improving swimming performance. To explore the effect of non-uniform flexibility on the motion performance of fish under biologically relevant conditions, we set up three different flexible distribution modes for a semi-free filament and compared the motion performance of different flexible distribution modes through numerical simulations. The filament is located in the wake of the front flapping foil; it can swing adaptively in the lateral direction according to the flow situation of the surrounding fluid and finally reach a stable position. The results show that the motion state of the filament will alter with a change in the flexibility of the filament, from moving in the vortex street to moving on the side of the vortex street. In the Benard-von Karman (BvK) vortex streets, the drag coefficient of the filament increases as the flexibility of the filament increases, and the value of the drag coefficient is at a minimum when the flexibility of the filament increases linearly along the length of the filament. Further investigation indicates that at 85%–90% of the filament length (starting from the leading edge), the flexibility of the filament begins to increase significantly, and the filament can obtain its best propulsion performance. The results of this work provide new insights into the role of non-uniform flexibility during the process of fish movement and provide a valuable reference for the design of bionic underwater vehicles.

In this paper, an adaptive state-feedback control technique is proposed for a class of unknown pure-feedback systems. A remarkable feature is that not only the problem of full-state constraints and prescribed performance tracking is solved together, but also the design is an approximation-free control scheme for pure-feedback systems with completely unknown nonlinearities. These properties will lead to a difficult task for designing a stable controller. To this end, a novel prescribed performance-barrier Lyapunov function is developed to guarantee that all the state constraints are not violated and the tracking error is preserved within a specified prescribed performance bound at all times, simultaneously. Then, by utilizing the mean value theorem, Nussbaum gain technique, a low-pass filter and a novel bounded estimation approach at each step of back-stepping procedure, a novel adaptive dynamics surface control scheme is developed to remove the difficulties of pure-feedback characteristic, unknown nonlinearities, unknown control direction and “explosion of complexity”, which can guarantee that the proposed design is universal and low-complexity. Moreover, it is proved that all the signals in the closed-loop system are global uniformly bounded. Two simulation studies are worked out to illustrate the performance of the proposed approach.

The propulsive performance of an oblique school of fish is numerically studied using an immersed boundary technique. The effect of the spacing and wiggling phase on the hydrodynamics of the system is investigated. The hydrodynamics of the system is deeply affected by the spacing between each fish in the school. When the horizontal separation is smaller than the length of the fish body, the downstream fish exhibits a larger thrust coefficient and greater propulsive efficiency than the isolated fish. However, the corresponding values for the upstream fish are smaller. The opposite behavior occurs when the horizontal separation increases beyond the length of fish body. The propulsive performance of the entire oblique school of fish can be substantially enhanced when the separations are optimized.

In this study, an adaptive dynamic surface control scheme is developed for a class of nonlinear systems. The considered systems can be viewed as a class of unknown pure feedback non-affine systems with multiple constraints. One remarked advantage is that not only less adjustable parameters are used in the design but also the design structure is universal for different systems. The characteristics of the considered systems will lead to a difficult task for design a low-complexity and stable controller. To this end, the mean value theorem is employed to transform the pure feedback systems into a linear structure, but non-affine terms still exist. Then, a novel recursive design procedure is constructed to remove the difficulties of unknown model, pure feedback non-affine characteristic and multiple constraints by integrating two auxiliary elementary functions with a novel bounded estimation approach. Furthermore, based on Lyapunov stability theorem and decoupled back-stepping method, it is proved that all the signals in the close-loop system are global uniformly bounded and the tracking error satisfies prescribed transient and steady state performance indexes constraints. Finally, simulation studies clarify and verify the approach.

Much of the bioactivities of Citrus flavanones significantly appear to impact blood and microvascular endothelial cells. It is essential to investigate the interaction between Citrus flavanones and serum albumin to verify the effect of flavanone structures on the distribution and transportation in blood. The interactions between flavonoids and proteins have attracted great interest among researchers. The work in here mainly concerns about the binding interaction between Citrus flavanones and human serum albumin (HSA) in vitro. The methoxylation of tangeretin improved the affinity for HSA by 100 times. The 2,3-double bond in conjugation with a 4-oxo group plays an important role for the affinity for HSA. The affinity of apigenin for HSA is about 10,000-times higher than that of naringenin. It was found that the hydroxylation on position 3' of flavonol significantly improves the binding affinity for HSA. The affinity of quercetin (3', 4') for HSA is about 100-times higher than that of kaempferol (4'). The hydroxylation on position 3' of flavone slightly improves the binding affinity for HSA. The affinity of luteolin for HSA is about 1.38-times higher than that of apigenin. The values of log10(Ka) are proportional to the number of binding sites (n), which confirms the method used here is suitable to study the interaction between Citrus flavanones and HSA.

Although petroleum exploration is being conducted in the Hong Kong region, high-quality hydrocarbon source rocks have never been found in this area. The Ping Chau Formation is only Mesozoic-Cenozoic sedimentary rock exposed in Hong Kong and its surrounding areas. The hydrocarbon source rock of the Ping Chau Formation is very rich in organic matters, which has an average total organic carbon (TOC) of 1.9% and chloroform bitumen “A” range from 0.14% to 0.24%. The total hydrocarbon content varies from 880 to 1800 ppm and the transformation ratio is specific from 5 to 9. The index of pyrolytic hydrogen is up to about 600 mgHC/gTOC. These data demonstrate the characteristics of the high-quality hydrocarbon source rock. The lamalginite is the major maceral of the source rock of the Ping Chau Formation, and geochemical characteristics also suggest that the organic materials of the source rock are of type I and type II1, with abundant gammacerane, γ, β-carotane and C24 tetracyclic terpane, which indicate that it was formed in the salt water and brackish water sedimentary environment, and the source rock has evolved into a mature phase. The organic inclusions are found within calcite veins in cracks of the source rock, indicating that hydrocarbon has been generated and a secondary migration has happened. The source rock in the Ping Chau Formation is about 200–300 m thick, thus having considerable hydrocarbon potential. The discovery of the high quality hydrocarbon source rock in the Ping Chau Formation will certainly provide insight on hydrocarbon resource exploration in the South China Sea area.